22 May 2008

CONTROL ALGORITHMS FOR SYSTEM INTEGRATION OF HEAT PUMPS: STEADY STATE AND SEASONAL ANALYSIS


This paper is concerned with the development of control strategies aimed at realtime
optimisation and system integration of heat pumps in building heating and cooling
applications. The research was motivated by the requirement to develop and implement
control algorithms for a reversible water-to-water ground source heat pump. This was
achieved by considering a secondary side control strategy, which examined the influence of
secondary fluid flow rates on both the heat pump and the integrated system performance.
Two control schemes were identified: (i) a Performance Maximisation approach, which was
achieved by adjusting the secondary fluid flow rates to settings that maximised COP
performance of the overall heat pump system, and (ii) a Capacity Maximisation approach
where the secondary fluid flow rates were set to their maximum settings, thus maximising the
heating or cooling capacity of the heat pump. A steady state model of the heat pump subject
to different water inlet boundary conditions, facilitated the development of performance
maps, thereby allowing the variation in heat pump capacity and compressor power
consumption with secondary fluid flow conditions to be examined. Further development of
the system model, to the include the ground and building system loops was undertaken,
thereby allowing overall system performance to be examined. Steady state and seasonal
performance simulations of the integrated heat pump, ground loop and building were
analysed. The two control schemes are compared in terms of their steady state and seasonal
performances and the modelled predictions are compared with experimental data collected
from a ground source heat pump installation.